Energy Problems During Marathon Training

I have been running for around two years now and I am right in the middle of training for my first marathon in about two months time. I run 5 times a week, but have had a couple of problems with energy during some recent training sessions...

For example last week I had to run 6M Intervals on Tuesday, 8M Steady on Wednesday and was heading out for 7M steady on Thursday. About 2 miles in to the 7M I started to feel tired and weak, a bit jelly-legged, hungry and cold.

Not the first time this has happened and all I could do was limp home at a reduced pace. I've examined my diet and fluids and think that I have a pretty good balance – I weigh 165lbs, consume around 1800-2000 calories per day and genuinely drink about 2 litres of water per day.

Any ideas what I am getting wrong or advice to help me with training?

Thanks in advance!

– Nick

Answer by Dom: Hi Nick, the jelly-legged, hungry, cold feeling partway through a run is classic bonking – and looking at your numbers, I think two separate things are going on: you're not fuelling the runs themselves, and 1800-2000 calories a day is very likely too low for what you're asking your body to do overall.

Here's what I want to cover:

1. Why this is happening now – the "monster month"
2. Your daily calories are probably too low
3. A concrete fuelling plan for runs over 90 minutes
4. Sleep, recovery and the finish line ahead

Why This Is Happening Now – the "Monster Month"

Marathon training is very tough and takes a lot out of you. I am not training for a marathon at the moment, but I have recently come back from an injury and am building up the mileage. My long run is getting to about 20-22km / 12.5-14mi, and I just notice that I am getting a little more tired as well.

This also leads to the occasional "unexplained bad run." One week you do the exact same run as the week before and suddenly you go a minute per km slower, or you have to stop in between. That's quite normal. They refer to that last stretch of marathon training before taper as the "monster month" – mileage is as high as it has ever been, some of the sessions are hard, and all of it adds up to extra tiredness.

But your description – jelly legs, hunger and cold arriving two miles into a run, on the third hard day in a row – points to something more specific than general monster-month fatigue. That pattern is a classic bonk: you're running out of readily available fuel mid-session.

Your Daily Calories Are Probably Too Low

At 165lbs and running five times a week including intervals, steady miles and a long run, 1800-2000 calories a day is on the low side – likely too low to properly fuel that volume, even before accounting for the extra burn from harder sessions like your Tuesday intervals. This is quite a common trap: runners assess their diet as "balanced" without weighing it against how much they're actually training.

I'm not going to hand you a precise target number – that depends on more than I know from your question – but I'd encourage you to eat noticeably more on your harder training days, and not treat every day of the week the same. A 6-mile interval session and an 8-mile steady run back to back need more coming in than a rest day does.

A Concrete Fuelling Plan for Runs Over 90 Minutes

This is the bit I think will make the biggest difference to how you feel mid-run. Feeling jelly-legged, hungry and cold only two miles into Thursday's run isn't really about that run's own length – it's about what came before it. Back-to-back hard days like your Tuesday intervals and Wednesday steady run can leave your glycogen stores under-stocked before you've even started the next session, so the wobble shows up earlier than you'd expect. Separately, for any single session that does run past 90 minutes, your muscle glycogen stores start running low regardless of how well-stocked you started – which is why fuelling during the run matters too, not just eating enough beforehand.

My advice: for runs that do tip past 90 minutes, aim to take in 30-60g of carbohydrate per hour once you're moving. Practically, that means:

• Start fuelling early – 30-45 minutes into the run, not when you first feel the wobble. By the time you feel it, you're already behind.
• Take it in small, frequent doses rather than one big hit – a gel or a few sports chews every 20-25 minutes works better than a large amount all at once.
• Practise this on your steady and long runs now, well before race day, so your gut is used to it by the time the marathon comes around.

Once your longer sessions are properly fuelled, that mid-run collapse should stop being a regular feature of your week.

Sleep, Recovery and the Finish Line Ahead

Alongside the food, make sure you get plenty of energy in via good foods generally, and don't skimp on sleep – when you are training seriously like you are, recovery is doing as much work as the sessions themselves. Also consider some extra "pampering" via a massage or so; it won't fix the fuelling gap on its own, but it helps you absorb the training load you're carrying right now.

Try to keep it going and know that taper is only a little while away. Fix the fuelling on your longer runs and eat a bit more on your hard days, and I'd expect these energy crashes to ease off well before then.

Best of luck in the upcoming marathon!

Kind regards,
Dom

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